The present invention relates generally to the field of heat exchanger tube bundle extractors, and more particularly to an aerial heat exchanger tube bundle extractor having an improved carriage or sled and motive means which are operable to move the tube bundle into or out of the heat exchanger shell.
Heat exchangers, such as are commonly employed in process plants or the like, typically comprise a cylindrical shell inside of which is disposed a bundle of elongate tubes. The shell may be twenty feet or more in length, and the tube bundle may weigh twenty tons or more. A circular plate known as a tube sheet is typically disposed on at least one end of the tube bundle. The tube sheet usually has a plurality of holes extending axially therethrough, and the open ends of the tubes will be affixed to the tube sheet so that each tube end is in fluid communication with one of the holes. Sometimes the tubes will be U-shaped, in which case each tube has two ends affixed to the tube sheet. In this arrangement, only one tube sheet need be employed. The tubes may instead be straight, and affixed to a tube sheet disposed at each end of the bundle. In either case, the tube sheet(s) is connected to other fluid flow apparatus such that fluids may be circulated through the tubes, into and out of the heat exchanger. Other fluids are caused to flow around the tubes inside the heat exchanger shell, thereby facilitating the heat exchange process between the fluids flowing through the tubes and those flowing through the shell.
The tubes and shell of the heat exchanger are subject to corrosion, deposition of mineral deposits and other build-up of foreign matter, both in and around the tubes and on the inside walls of the shell. These deposits need to be removed on a regular basis, because they interfere with the heat exchange process and reduce the efficiency of the heat exchanger. In order to effectively remove the deposits, the tube bundle must first be removed from the shell, so that all exterior surfaces of the tubes, and all the inside surfaces of the shell, are accessible in the cleaning operation. Once removed, the tube bundle may be cleaned at the plant site in special equipment transported on-site for that purpose, or transported to a remote cleaning facility. The shell, which may be located several stories above the ground, is typically cleaned in place.
Removal and reinstallation of tube bundles for cleaning or for other purposes (e.g., repair or replacement) are typically accomplished with a tube bundle extractor having an elongate chassis for supporting a tube bundle when removed, a means for engaging the tube bundle, and a means for alternately applying a pulling force or a pushing force to the tube bundle to withdraw the tube from, or to insert the tube bundle back into, the shell. The extractor will also include a means for engaging the shell or other fixed structure for carrying reaction forces arising during the bundle pulling or pushing operations.
One approach used in the past toward creating the relatively high pushing and pulling forces required for moving a tube bundle includes providing one or more rotatable drive screws extending longitudinally through most of the length of the chassis, in engagement with one or more nuts fixedly disposed on a movable sled. The sled will be adapted for movement on the chassis, such as by sliding or rolling along a track, so that when the drive screw is rotated one way or the other, the sled is caused to advance or retreat, as the case may be, along the chassis. The sled will be engaged with the tube bundle so that movement of the sled along the chassis caused by rotation of the drive screw pulls the tube bundle from, or pushes it into, the shell. See, e.g., U.S. Pat. No. 4,869,638, issued Sep. 26, 1989, to Krajicek et al. Another approach used in the past in tube bundle removal and replacement includes providing a rotatable pinion on the sled in engagement with a fixed rack on the chassis. See, e.g., U.S. Pat. No. 4,392,524, issued Jul. 12, 1983, to Bauch.
In prior art arrangements such as those disclosed in the Krajicek and Bauch patents, at least some of the equipment comprising the prime mover or power source, and/or the power conversion apparatus, and/or the power transmission apparatus is disposed on the chassis of the extractor, while other components of such power systems such as hydraulic motors, hydraulic cylinders, or the like are disposed on the sled. Because the sled of an extractor is movable with respect to the chassis, this usually requires that a sometimes complex system of cabling, piping, hoses, and the like be provided for communicating between chassis and sled so that all powered systems remain operative as the sled traverses the chassis. In other words, usually the sled must be continuously connected to the chassis by often complex, often bothersome or in-the-way `umbilical lines` in order to ensure that all powered systems are properly supplied at all times with needed hydraulic fluid or the like. When flexible hoses, such as rubber hoses or the like, are used for such `tethering` operations, they will have to be maintained and/or repaired from time to time, and eventually replaced; this of course increases operating costs.
In U.S. Pat. No. 3,836,015, issued Sep. 17, 1974, to Travis, there is disclosed the use of a fixed chain on the chassis engaged by a sprocket on a rotating shaft of a rotary motor on the sled to enable the sled to walk along the chain; and the use of a fixed rack on the chassis engaged by a pinion on the sled, the pinion also being driven by a motor, M, on the sled. There is also disclosed a relatively larger hydraulic cylinder and piston mounted on the sled, referred to by the patentee as a prime mover and serving as a linear actuator, for applying a breakout force to the tube bundle and for moving the tube bundle initially along the chassis. However, the nature and location of the power generation, conversion, and control equipment for powering and operating the rotary motors, and the linear actuator hydraulic cylinder, are not disclosed in the Travis patent.
U.S. Pat. No. 3,490,609, issued Jan. 20, 1970, to Poole, and U.S. Pat. No. 2,650,728, issued Sep. 1, 1953, to Goodwyn, disclose use of an internally threaded rotating nut or gear within which is disposed a threaded rod for the purpose of causing longitudinal movement of the rod. The Poole patent uses the moving rod to actuate the ram head of a pipe laying sled, and the Goodwyn patent uses the moving rod to adjust the bumper lugs of a transfer bar of an automobile storage apparatus.
Other examples of tube bundle extractors are shown, for example, in U.S. Pat. No. 4,358,242, issued Nov. 9, 1982, to Davies, and U.S. Pat. No. 3,567,044, issued Mar. 2, 1971, to Travis.